Physio Lab 7.2-7.4

What are the normal values for the P-R interval

.12 - .20 seconds

What is third degree AV block and how is it relative to the ECG

A complete AV node block meaning none of the atria electrical waves can pass through the AV node to the ventricles. This causes the ventricles to beat at 20-40 BPM (bradycardia). The QRS wave and T wave are a bit abnormal

What is second degree AV block and how is it relative to the ECG

A severe damage to the AV node and only every other two to three atrial electrical waves can pass through to the ventricles causing the heart to skip beats. On the ECG it shows the presence of P waves without QRS waves associated

What is first degree AV block and how is it relative to the ECG

A slower than normal conduction of the AV node (because of damage of AV node) that exceeds .20 seconds shown at the P-R interval

What happens to parasympathetic vs sympathetic activity in the heart at the start and during exercise

At the beginning of exercise the activity of the parasympathetic fibers that innervate the SA Node decreases which increases the cardiac rate. As exercise becomes more intense the activity of the sympathetic fibers that innervate the SA node increases producing an excitatory effect on the SA node which causes an even greater increase in cardiac rate

Electrical event of the P wave

Atria depolarization

What is the normal mean axis of the ventricles

Between 0-90 degrees and found in ventricles

Abnormal slow HR

Bradycardia

Electrical event of the T wave

Depolarization of ventricles

The electrical synapses between adjacent myocardial cells

Gap junctions

What are the main and secondary causes of increased cardiac rate during exercise and how are they represented on the ECG

Main cause is due to a shortening of ventricular diastole from peak of T wave to beginning of QRS complex. Secondary cause is shortening of ventricular systole from QRS peak to peak of T wave

The ECG wave completed just before the end of ventricular diastole is

P or (Q) wave

The ECG wave that occurs at the beginning of ventricular systole is the

QRS or (R)wave

Which ECG must occur before the ventricles can contract

QRS wave

The pacemaker region of the heart is

SA Node

The ECG wave that occurs at the end of systole and the beginning of diastole is the

T wave

Abnormal fast HR

Tachycardia

Describe the pathway of conduction from the atria to ventricles and correlate this with the ECG waves

The SA node sends signal through atria via gap junctions causing the atria to depolarize which is the P wave following atrial contraction. After a brief delay allowing time for the ventricles to fill up the AP's from the SA node stimulates the AV node which sends a signal to the R and L bundle branches to the purkinje fibers causing depolarization shown as the QRS wave and is followed by ventricular contraction. The Ventricles relax and depolarizes and this is the T wave.

What does the mean axis show

The average direction of depolarization

What changed the most on the CG as you went from resting to exercise to post exercise and what changed the least

The magnitude of the P wave increased and the T wave increased. As well as the shortening of contraction and relaxation of ventricles. The QRS complex remained the same

Describe the pressure changes that occur within the ventricles as each ECG wave is produced and how are they related to the ECG waves

The pressure increases when the ventricles contract between the R and T wave and pressure decreases when the ventricles are relaxed from the peak of T wave to QRS wave.

Electrical event of the QRS wave

Ventricle depolarization